PowerPoint is undoubtedly a useful tool, but it is much abused, and while anyone can produce ugly looking slides which hinder communication, producing good slides which do the job is much more complicated.
Fortunately there are many resources available to help you learn the common sense and cognitive science behind good design.
1 – Take a look at the links below
From a physics lecturer : This is mostly aimed at lecturers, but some of the tips will be useful
Handout from a training workshop : This is also a resource for educators, but very well done.
Tips from a graphic design blog : Part 1, Part 2, Part 3
2 – download this extremely ugly civil engineering presentation, and working in pairs see if you can improve it.
3 – Send your version to me at the end of the session